Asunción Santamaría

An application of the SMS method for imaging designs

The Simultaneous Multiple Surface (SMS) method in planar geometry (2D) is applied to imaging designs, generating lenses that compare well with aplanatic designs. When the merit function utilizes image quality over the entire field (not just paraxial), the SMS strategy is superior. In fact, the traditional aplanatic approach is actually a particular case of the SMS strategy.

Free-form optics for Fresnel-lens-based photovoltaic concentrators

The Concentrated Photovoltaics (CPV) promise relies upon the use of high-efficiency triple-junction solar cells (with proven efficiencies of over 44%) and upon high-performance optics that allow for high concentration concurrent with relaxed manufacturing tolerances (all key elements for low-cost mass production). Additionally, uniform illumination is highly desirable for efficiency and reliability reasons. All of these features have to be achieved with inexpensive optics containing only a few (in general no more than 2) optical elements. In this paper we show that the degrees of freedom using free-forms allow the introduction of multiple functionalities required for CPV with just 2 optical elements, one of which is a Fresnel lens.

Free-form integrator array optics

A new design method of free-form Kohler integrator array optics is presented. Only few solutions to the integrator design problem are known, which apply for specific and simple source and targets (for instance, flat integrator lenslet arrays when the source and target are squares located at infinity). The method presented here find more general solutions and the resulting optics is formed by two arrays of free-form optical surfaces (which can be either reflective of refractive). The contour curves of the array units are also obtained from the design. Two types of Kholer integrators will be defined, depending if they integrate only along one direction across the source (one-directional integrators) or in the two directions (two-directional integrators). This design method has been applied for an ultra-compact high efficiency LED low beam head lamp producing a legal pattern independently of the chip luminance variation and permitting LED position tolerances of ±200 microns. The ray tracing proves that the high gradient (0.32) and its vertical position in the pattern remain invariable when chip is moved.

Overview of the SMS design method applied to imaging optics

The Simultaneous Multiple Surfaces (SMS) was developed as a design method in Nonimaging Optics during the 90s. Later, the method was extended for designing Imaging Optics. We present an overview of the method applied to imaging optics in planar (2D) geometry and compare the results with more classical designs based on achieving aplanatism of different orders. These classical designs are also viewed as particular cases of SMS designs. Systems with up to 4 aspheric surfaces are shown. The SMS design strategy is shown to perform always better than the classical design (in terms of image quality). Moreover, the SMS method is a direct method, i.e., it is not based in multi-parametric optimization techniques. This gives the SMS method an additional interest since it can be used for exploring solutions where the multiparameter techniques can get lost because of the multiple local minima.

High-efficiency LED backlight optics designed with the flow-line method

A novel backlight concept suitable for LEDs has been designed using the flow-line design method, which allows controlling both the illumination uniformity and light extraction without scattering the light. This contrasts with conventional LED backlight optical designs, which are based on the use of a light guide with Lambertian scattering features that break the guidance and extract the light. Since most of Lambertian scattered light is re-guided, the average ray path in conventional backlights is long and multiple bounces are needed, which may lead to low efficiency. On the other hand, the new design presented here is not only efficient but also provide a relatively high collimation of the output beam (an output beam within a 10 degrees half-angle cone, with total theoretical efficiency over 80% including Fresnel and absorption losses). Wider beams can be controlled by design or obtained by adding a holographic diffuser at the exit. The new design offers other very interesting practical features: it can be very thin, can be made transparent (which widens its applications, including front lighting), can mix the colors from several LEDs or recover reflected polarization for LCD illumination.

High-efficiency free-form condenser overcoming rotational symmetry limitations.

Conventional condensers using rotational symmetric devices perform far from their theoretical limits when transferring optical power from sources such as arc lamps or halogen bulbs to the rectangular entrance of homogenizing prisms (target). We present a free-form condenser design (calculated with the SMS method) that overcomes the limitations inherent to rotational devices and can send to the target 1.8 times the power sent by an equivalent elliptical condenser for a 4:1 target aspect ratio and 1.5 times for 16:9 target and for practical values of target etendue.

Novel ray-tracing approach for fast calculation of the impulse response on diffuse IR-wireless indoor channels

In this paper, a modified Monte Carlo algorithm for the calculation of the impulse response on infrared wireless indoor channels is presented. This work follows a guideline of studies about the infrared wireless diffuse data communications systems. As is well known, the characteristics of the room where the IR diffuse channel is implemented determine some problems in the communication as can be multipath penalty over the maximum band rate or hidden station situations. Classical algorithms require high computational effort to calculate the impulse response in a regular size room. Monte Carlo offers the possibility of validating the assumptions made for these classic algorithms (basically, the lambertian nature of all reflections) with a computational complexity that is decided by the accuracy desired by the user. It is also an structure that can be easily assumed by a parallel computer architecture. In the other hand, its main drawback is that, for a regular sized room, we need to send much more rays than the components that we receive. This is due to the fact that usually rays are not intercepted by the receiver. We have developed a mixed Monte Carlo-Deterministic algorithm which assures that each ray contributes to the final channel response function each time it rebounds with an obstacle. It increases dramatically the number of contributions and reduces, in the same way, the time required for an accurate simulation. Extensive simulation results are presented. They are compared both with other simulation methods and with measured values. We will demonstrate that the method presented here is much faster than Monte Carlo classical simulation schemes. It can be used like a method of simulation itself or as a validation algorithm for other comparative studies of pulse broadening.

Advanced PV concentrators

It is essential to obtain high values of tolerance for PV concentrators because manufacturing process always implies some accuracy errors. In this way, three new free-form concentrators are presented here, combining high geometric concentration and high tolerance (high acceptance angle). This is achieved by using the SMS3D design method, which is the most advanced method to design free-form surfaces in non-imaging optics. Uniform illuminance on the cell is important as well, for proper behavior and durability of the system, so our three designs will have homogenizer elements. We have added a homogenizer rod to one of the designs while for the other two Ko¿hler integrator configurations have been chosen. Concentration, acceptance angle and uniformity values obtained are shown in results section.

Next generation of Energy Residential Gateways for Demand Response and Dynamic Pricing

Predictions about electric energy needs, based on current electric energy models, forecast that the global energy consumption on Earth for 2050 will double present rates. Using distributed procedures for control and integration, the expected needs can be halved. Therefore implementation of Smart Grids is necessary. Interaction between final consumers and utilities is a key factor of future Smart Grids. This interaction is aimed to reach efficient and responsible energy consumption. Energy Residential Gateways (ERG) are new in-building devices that will govern the communication between user and utility and will control electric loads. Utilities will offer new services empowering residential customers to lower their electric bill. Some of these services are Smart Metering, Demand Response and Dynamic Pricing. This paper presents a practical development of an ERG for residential buildings.

On the analysis of rotational symmetric microstructured surfaces.

A previous paper [2] presented an analysis of a class of microstructured optical surfaces in two dimensions, in which a classification of the microstructures was obtained (regular and anomalous) and a concept of 2D ideal microstructures was introduced. In this paper the study of those microstructured optical surfaces is extended to three dimensions with rotational symmetry. As a starting point, non-microstructured rotational optical systems in the First Order Approximation are also classified as point-spot type and ring-spot type, with remarkable perfect particular cases. This classification is also extended to the case in which ideal microstructured rotational surfaces are used, for both regular and anomalous type. The case of perfect ring-spot type system with an odd number of rotational, anomalous, ideal microstructures enables the definition of an anomalous aplanatic system that has direct application for mixing spatially and angularly the light emitted by several sources.